The world's largest internet players are jockeying for position in voice-activated search services as they strive to extend their reach beyond computers to mobile phones.

With mobile advertising revenues forecast to grow eightfold in the next four years, to $11.5 billion (£5.8 billion) and the market for directory enquiries worth $8 billion a year in the US alone, Google, Yahoo! and Microsoft, the leaders in web search, are all targeting the sector.

Competition hit a new pitch after Google unveiled a telephone-based service that allows users to dial a number and vocally request details for local businesses in American cities. Google Voice Local Search uses voice-recognition technology to process queries and delivers answers using Google Maps.

The move comes only weeks after Microsoft agreed to acquire Tellme Networks, a privately owned specialist in voice-recognition technology, for an estimated $800 million.

Tellme already has deals to supply voice-activated information such as stock quotes and weather updates to groups including AT&T and Verizon Wireless, the joint venture between Verizon Communications and Vodafone.

The world’s largest software group has already demonstrated its commitment to voice technology at its “home of the future” site based at its headquarters in Redmond.

The model house, designed to showcase technologies that Microsoft believes will be viable within a decade, is activated by Grace, a listening, speaking interface.

Yahoo! is also staking its claim to the mobile market through its oneSearch product, which is tailored to handheld devices and will be rolled out in Europe this month.

Yahoo! is yet to deploy voice-recognition services, but the group recently hired two executives from Tellme. Geraldine Wilson, who heads Yahoo's Connected Life division, which includes mobile services, in Europe, said: "Voice interaction is a logical extension to oneSearch."

Yahoo!, which has been berated for falling behind Google in traditional search services, is also thought to be working on a mobile-based social-networking service, which would seek to replicate the success of sites such as Facebook and Bebo.

A Google spokesman said that Google Voice Local Search “really is totally experimental at this stage”, adding that the company has no plans to offer it outside the US.

However, the company has recently focused on broadening its mobile footprint, most recently by signing a deal to pre-install its software in LG mobile phones.

Google is also thought to be working on its own operating system for mobile phones, and possibly its own branded handset.

Google Voice Local Search does not charge users for the information but they will be charged by telephone companies for making a phone call or receiving a text message of results.

Users can then search by saying a business name or a category of service — for example, "Giovanni's Pizzeria" or "pizza San Francisco". Users can say "text message" to receive details by SMS if using a mobile phone.

The service follows a broader trend towards advertising-supported telephone information services.

In 18 months, Jingle Networks has captured 5 per cent of the directory enquiries market in the US, forwarding more than 200 million calls. The company's backers include Goldman Sachs and Comcast Interactive Capital, a division of Comcast, the largest US cable provider.

The company does not charge for information, but its users do have to listen to an advert.

Meanwhile, internet groups have rushed to have their software pre-installed on mobile handsets as they seek to capture market share.

Microsoft has signed up LG Electronics, Toshiba and Hewlett-Packard to build handsets that would run on its Windows Mobile operating system.

Yahoo! already has deals with Nokia, Motorola, RIM, LG and Samsung, the handset manufacturers, to have its software shipped on certain handsets.

It also has a partnership with HTC, a Taiwan-based company that has been named as a possible partner to Google in its mobile plans.

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